The present invention relates to a control device and a method for adjusting the angular velocity ratio (ωN(t)/ωK(t)) between a camshaft and a crankshaft.
In internal combustion engines, the crankshaft drives one or more camshafts via a primary drive, which is implemented as a toothed belt, for example. For this purpose, a cam wheel, via which the primary drive drives the camshaft, is attached to each camshaft. The angular velocity ωK(t) of the crankshaft is converted at each instant, whereby the angular velocity of the crankshaft ωK(t) can be used in determining the angular velocity of the camshaft ωN(t), using ωN(t)=½*ωK(t). The ratio of the two angular velocities is constant due to this coupling. In most applications, this fixed coupling between camshaft and crankshaft results in a ratio of (ωN(t)/ωK(t))=½.
However, the operating properties of an internal combustion engine may be optimized, particularly in regard to fuel consumption, exhaust gas emission, and smooth running, if the system coupled between the camshaft and crankshaft via the primary drive may be altered.
A control unit for adjusting the rotational angle of a camshaft in relation to the rotational angle of a crankshaft using a wobble plate mechanism is disclosed in DE 100 38 354 A1. In this case, an additional drive also acts on the camshaft via a wobble plate mechanism which is positioned between the cam wheel and the camshaft. This results in the camshaft being able to be adjusted in relation to the crankshaft. The additional drive may act on the camshaft in both directions via the wobble plate mechanism, so that its angular velocity in relation to the camshaft, and therefore the fixed ratio (ωN(t)/ωK(t)), changes.
However, this has the disadvantage that the drive must have right-handed rotation and left-handed rotation, in order to move the wobble plate both in one direction and in the other direction, or two motors which have different rotational directions are necessary. In the event of sudden changeover from one rotational direction to the other rotational direction in order to return the camshaft into the original starting position, for example, all components are strongly loaded and, in addition, in the case of electric motors which have right-handed rotation and left-handed rotation, bridge circuits are then necessary, which require costly power components.